Cellulosic structure



Patented Sept. 7, 1943 CELLULOSIC STRUCTURE Henry Shirley Rothrock,.Wilmington, Del., as- Y signor to E. I. du Pont de Nemours & Company,vWilmington, DeL, a corporation of Delaware No Drawing. Application May6, 1941, Serial No.

2 Claims.

This invention'relates to cellulosic structures, especially those'ofpellicular nature. More particularly, it relates to a method forproducing flexible and durable cellulosic pellicles by treating the samewith softening agents comprising polymerized alkylene oxide, and theproducts resulting from such treatment. I

This application is related to my copending application Serial No.392,116, filed of even date herewith. v i

In the manufacture of cellulosic pellicles of the type precipitated fromaqueous solutions such as regenerated cellulose pellicles, includingsheets or films, caps. bands, continuous tubing, artificial straw andthe like, ithas long been customary to incorporate into the cellulosicpellicles a softening agent inorder to maintain them in a flexiblecondition. Such cellulosic pellicles when freed from a softening agentare known to be quite brittle, and while a softener-free pellicle mayfind certain uses, a softened and, therefore, flexible sheet or film ismuch more generally useful.

Heretofore, as softeners for the cellulosic pellicles, the art hasapplied such substances as ethylene glycol, propylene glycol, diethyleneglycol, formamide, glycerol, and the like, but of these it is found themost important is glycerol which has hitherto known no equal as a'softening agent for producing flexible, transparent and durablecellulosic pellicles such as those of regenerated cellulose.

However, glycerol and other softening materials used heretofore for thesoftening of regenerated cellulose products possess two serious dis-'advantages, namely, volatility and a tendency to transfer or migrate toother materials in contact with the softened regenerated cellulose.- Itis generally truethat if the concentration of softener is too, high, thecellulosic pellicle will be unduly limpand sticky, whereas if the concentration is toolow, the article will be brittle and lack durability. Aneffort is, therefore, made at the time of manufacture toincorporate-substantially the correct amount of softener to obtain thephysical properties desired in the final film.

However, in the case of a pellicle with a large area exposed to theatmosphere for long periods of time, even those softening agents whichhave a very low butappreciable 'vapor pressure will in time escape to asufficient degree to lower the concentration of softener'in the filmbelow that addition result in certain shrinkage and distortion of thepellicle making it unfit for use.

Difficulties arising from a decrease in softener content may also bebrought about in quite a different manner than the escape of thesoftener through volatilization. It has been observed that regeneratedcellulose products, which are in contact with other cellulosic bodieshave a tendency to lose their softening agent when this agent is of thevolatile or migrating type represented by those materials referred toabove and, in fact, most of the softening agents heretofore known. As anexample, cellulosic products such as paper, cotton, and linen fabrics,etc., wrapped in thin pellicles of regenerated cellulose softened withglycerol are found after a short time to extract a large portion of theglycerol from the pellicle used as a wrapping tissue leaving the latterbrittle and distorted. This is a serious restriction in the use of thesematerials for wrapping a large number of products which may otherwiseadvantageously be wrapped in such transparent tlSSue. C I

Similarly, it has been proposed to cover wooden forms in the shape ofbobbins, spindles, and guiding members with a sleeve of regeneratedcellulose shrunk into close contact with the surface of the wooden form.Where such forms are subsequently wrapped with fabric or yarn, theglycerol or other softener soon makes its escape on the one side to thewooden core and Y on the other side to the cellulosic materials wrappedor placed over the core. As a result,

the cellulosic sleeve soon shrinks and crack and must be replaced.

Certain softeners which have been suggested in the past to producespecial effects are, in general, unsatisfactory for commercialproduction of film because of water insolubility. -while it is true'thatit is possibl to introduce softening 7 materials into regeneratedcellulose products by at which satisfactory softening action isobtained. A reduction of only a few per cent in the softener content mayresult in the deleterious reduction of flexibility and durability andinsoftened cellulosic materials possessing special methods, the methodordinarily. employed in the production of the regenerated celluloseproduct requires water solubility of the treatin material; the use ofspecial methodsfor the introduction'of water insoluble-materials leadsto prohibitive costs in the manufacture of the cellulosic product. Itis, therefore, an object of this invention to provide a new and usefulmethod for producing desirable physical properties. It is a furtherobject to provide cellulosic materials having a softening agentassociated therewith, which softening agent will not tend to escapethrough volatilization or through transfer to other cellulosic bodies.

Other objects of the invention will appear hereinafter.

The objects of this invention can be accomplished, in general, bytreating a water-sensitlve cellulosic pellicle, such as a regeneratedcellulose pellicle, with an aqueous solution or dispersion of a polymerof 'an alkylene oxide, which process, the viscose dispersion is extrudedthrough a fine slot into a coagulating and/or regenerating bath fromwhich it is finally obtained in the form of a continuous cellulosicsheet, which is customarily led in a continuous manner through a seriesof purifying, bleaching and washing operations, as described inBrandenberger, U. S. Patent No.-1,548,864. In certain cases, the viscosesolution is extruded and processed in the form of a tube by well-knownmethods of operation. Just prior to the drying operation, which is alsousually continuous, coordinating with the extruding operation, the filmis passed through a bath containing a softening agent in suchconcentration that after the excess liquid has been removed from thesurface of the sheet by suitable squeeze rolls and the excess moistureremoved by passage through the drier, the web can be wound up in acontinuous fashion and will contain an appropriate, predetermined amountof softening agent.

The commercially available regenerated cellulose film containsapproximately 4% to 8% moisture, depending upon the softener content andthe relative humidity of the atmosphere. Depending'upon the use of thefilm, the softening agent contained therein, usually glycerol, may varyfrom about-8% to 25%. based on the combined weight of the cellulose andsoftening agent perature of the bath, etc., may also contribute to acertain extent. The regenerated cellulose pellicle, when reaching thetreating bath is in a highly swollen and hydrated condition and usuallythe cellulose of the pellicle is associated with 300% or more of water,based upon the weight of the cellulose. This highly swollen and wetpellicle, usually referred to as the gel sheet, is impregnated with thetreating bath. Because of the large amount of water associated with thecellulose, it isapparent that the removal of this water during thedrying operation will concentrate the softening agent with respect tothe cellulose content of the pellicle.

It has now been discovered that polymers of alkylene oxide having amolecular weight in the range of 400 to 5,000 and which exhibit asolubility in water at 25 C. of at least 4% are eminently suited for thepurposes of this invention. In some instances, the polymers may containmodifying groups as hereinafter specified.

The polyalkylene oxide used in the process of this invention may beprepared by any of the known methods, for example by heating themonomeric oxide in the presence of a catalyst (e.

\ g., an alkaline catalyst) if necessary under pressure, until asubstantial proportion of polymer is formed, and removing the unchangedmonomer.

.Staudinger, Die Hochmolekularen Organischen Verbindungen, 1932,'page287 et seg.) The products, depending on their molecular weight, aresolid, semi-solid, or even fluid materials, which are soluble in bothwater and certain organic solvents such as benzene. These products aregenerally believed to be composed of a plurality of alkylene groupslinked together in linear configuration through ether linkages, and tobear hydroxyl groups at the ends of the polymeric chain. Thus,polyethylene oxide is represented by HO(CH2CH20) nCH2CH2OH (Staudingerloc. cit.). These polymers are sometimes called polyethylene glycols.

Commercially prepared polyalkylene oxides, such as the materialsproduced by the Carbide and Chemicals Corporation under the trade nameCarbowax are satisfactory for the process of this invention.

The molecular weight of the polyethylene oxide used is a critical factorand it is therefore necessary to use products having a molecular weightnot substantially in excess of 5,000 since higher molecular weightproducts become less soluble and less easily dispersible in thecellulosic material. It is 7 also necessary, for satisfactory results,that the molecular weight of thepolymers be above 400 since those oflower molecular weight are, to some extent, volatile and tend to migrateor transfer out of the regenerated cellulose product to other cellulosicmaterials with which the same may be in contact.

Although the polymeric alkylene oxides themselves are to be preferred inthe practice of this invention, a number of materials composed of a apolymeric alkylene oxide having certain constituents attached to one endof the molecule, for example, such as methyl cellosolve (beta methoxyethanol) or castor oil, are useful in the practice of this invention.

It has been pointed out by Flory, JACS, volume 62, page 1561 (1940),that ethylene oxide reacts with ethylene glycol to form diethyleneglycol and higher glycols by successive additions of ethylene oxide on achain basis. In a similar manner, the ethylene oxide will form reactionproducts with castor oil and other materials having hydroxyl groups.

The following examples are given-to illustrate the preferred methods ofcarrying out the present invention. The parts and percentages referred.to are parts and percentages by weight.

Example I Excess liquid is removed from the surface of the sheet bymeansof squeeze rolls, doctor knives, etc. and the sheet dried on theconventional roll drier. After drying, the sheet is found to contain 13%polyethylene oxide, based on the weight of the cellulose. andapproximately 6% water.

The sheet so produced is transparent, flexible V and durable, and theflexibility of the sheet --is not substantially impaired when usedinwrapping of paper or fabricgoods;

I Example II t A sheet prepared as in Example I, is passed through abath containing i11% polyethylene oxide (Carbowax" with an'averagemolecular weight of 4,000), excess solution removed from the surface ofthe web, and the same dried in Example III- A sheet produced as inExample I is passed through a bath containing 7% of the reaction productof 4 parts of ethylene oxide polymer and 3 parts of glycerol (parts byweight). Excess solution was removed from the surface of the sheet andthe same dried in the usual manner. The final product contained 13% ofthe softening agent and was highly flexible, transparent and durable.

Example IV A sheet prepared as in Example I' is passed through a bathcontaining 11% of a condensation product of ethanol formamide andethylene oxide, said condensation product containing one mol of ethanolformamide per mol of po ymer.

and having an average molecular weight of 469.

Excess solutionis removed from the surface of the sheet and dried in theconventional manner. The sheet so produced contains 17% of the softeningagent and is highly flexible, durable and transparent. I

Example V A sheet produced as in Example I is passed through a bathcontaining 7% of the reaction product of glycerol and ethylene oxidepolymer having an average molecular weight of 461. Excess solution wasremoved from the surface of the sheet and the same dried in the usualmanner. The final product contained 13% of the softening agent and washighly flexible, transparent and durable.

Example .VI

Example VII A sheet produced as in Example I is treated with a bathcomprising 7% of the reaction product of tetrahydro furfuryl alcohol andethylene oxide, said products having an average molecular weight ofapproximately 721. The product after removal of excess liquid and dryingcontains approximately 13% of the softening agent to-. gether with 6%moisture, based upon the cellulose. It is highly transparent, flexibleand durable.

, parent.

Example VIII.

" z A sheet produced as in Example I is passed through a bath containing.11 of thereaction product of cetyl alcohol and ethylene. oxide, saidreaction product having an average molecular weight of approximately480.; After removal of excess liquid and drying, the sheet is found tocontain approximately 17% of the softening agent and is highly flexible,durable and trans- Example IX A regenerated cellulose pellicle in theform of a tube is coagulated, regenerated and purified in a mannersimilar to that described in Example I wlthreference to the productionof a regenerated cellulose sheet. The tube is then passed I through abath containing 11% of the'reaction neck of the bottle.

product of methyl cellosolve (beta methoxy ethanol) and ethylene oxidepolymer, said reaction product having an average molecular weight ofapproximately 783. Excess liquid is removed from the surface of thetube, the'same cut into short lengths and applied to the mouth and neckof a liquor bottle as a secondary closure. Uponevaporation' of themoisture, the band shrinks into intimate contact with theneck of thebottle serving to protect the cork or other primary closure and theupper portion of the This cellulosic band is in contact with the paperliquor stamp with" which such bottles are provided. It is found thateven .after long periods of storage the softeningmaterial does nottransfer from the cellulosic band to the paper of the tax stamp andhence the cellulosic band is. not embrittled or otherwise deleterlouslyaffected so as to cause its premature removal from the bottle. Longersections of tubing prepared in this manner may be very satisfactorilyshrunk onto wooden cores used as bobbins and forms for the winding oftextile yarns.

As a base, the invention contemplates the use of any non-fibrous,water-sensitive cellulosic structure, particularly of pellicular naturesuch as a sheet or film, artificial straw, caps, bands, or continuoustubes, such as may be obtained by the coagulation and/or regenerationfrom an aqueous alkaline cellulosic dispersion in an acid coagulatingbath in accordance with the procedure customary to the art. Thus, theinvention comprehends the use of regenerated cellulose pellicles such asmay be obtained from viscose or cuprammonium cellulose, glycolcellulose, cellulose glycollic acid, lowly esterified or lowlyetherifled cellulose derivatives whereth'ere is only one ether or estergroup associated with several cellulose units, and other cellulosicstructures of similar character.

All of the examples given have been set forth in terms of a sheet orfilm of gel regenerated cellulose (gel regenerated cellulose is a waterswollenv regenerated cellulose which never has been dried). Obviouslythis is the more practical way of practicing the invention since th'esoftening agent is customarily incorporated into the,

composition suitable to obtaining'the final prod uct desired.

In general, the softening materials comm-e hendedv by this invention arethose that areformed by'the polymerization or chain reaction of analkylene oxide such, for example, as ethylene oxide, propylene oxide,butylene oxide, etc.

said chain formations to extend to products with a molecular weightlying in the range of 400 to 5,000. The products of interest in thisinven tion are those having'a water solubility atza temperature of'25 C.of at least 4% in order that they may be introduced in a satisfactorymanner into the regenerated cellulose or other -example,,aliphaticacids, amines, hydroxylated materials such as glycerol, ethyl cellosolve(beta ethoxy ethanol), etc. .In general, the softening material will beformed by reacting the modifying group with ethylene or other alkyleneoxide until the molecular weight of the resulting product lies in therange of 400 plus the molecular weight of the modifying group to 5,000plus the molecular weight of the modifying group. Modifying groups ofespecial interest to this invention areas follows: 'adipic acid, castoroil, aniline, glycerol, methyl cellosolve (beta methoxy ethanol),N-isobutyl acetamide, bis-N,N'-ethyl ethanol urea,N-butyl-N-beta-hydroxy ethyl lactamide, bis-N,N' -ethanol oxamide,glycerol furfural, glycerol formal, 2,2-diethyl-1,3-propanediol.

It is also to be understood that various mixtures of the newly describedsoftening agents may be employed with single softeners of the prior artor with mixtures of the latter, depending uponthe type of final filmdesired and the purposes for which the film is to be used. Othersoftening agents suitable for incorporation with the softeners of theinvention. are as follows:

ethylene glycol, ethanollactamide, isopropanolglycolamide,ethanolformamideeethylene oxide reaction product of an 'apparentmolecular weight of 152, aniline-ethylene oxide reaction product of anapparent molecular weight of 244, etc.

If a. colored cellulosic pellicle i desired, it may be obtained-in anyof the ways commonly known in the art, including the passage of thesheet or film through a bath containing a suitable dyestufl. If desired,the dyestuff maybe added, to r the bath used for introducing thesoftening agent. In the same way, after the film has been treated withthe softening agent, it may be subjected to any of the customary aftertreatments such as 818111801 coating or. theiike, which may be cus-vtomarlly given to cellulosic pellicles of the type described, in justthe same manner that a glycerol softened regenerated cellulose film, forexample, may be treated. v

The term "durability" as used in the present specification refers toresistance to shock or rough handling. Thus, for example, bags may befabricated from the pellicle and filled with some standard material suchas a certain weight of dried beans, and the package sealed, whereuponthe durability may be measured, by dropping the package under standardconditions and notingthe resistance to breakage of the wrapper.

The outstanding advantage of the softening agents of this invention overthose described in the prior art is the permanence with which theyremain in a non-fibrous cellulosic structure. Since they are of very lowvolatility, they are not lost by volatilization such as a number of wellknown softeners, for example-glycol and glycerol. Furthermore, they donot migrate or transfer out of the transparent cellulosic structure toother cellulosic structures with which the same may be in contact; Thislast named property permits use of these material in the form of thinpellicles a's wrappings with cellulosic materials, for example, fabrics,textiles, paper, etc., and permits their long and continued contact withthe contents of the package without losing the softening agent andconsequently with the retention of the flexibility. and durability ofthe original wrapping tissue. As another example, caps and bands usedassecondary closures for containers may be applied to the mouths andnecks. of bottles over paper labels and still exhibit no tendency toembrittlement, splitting and cracking after long periods of storage;Similar cellulosic tubing may be employed as durable and lastingprotective coverings for wooden cores and bobbins,- etc.

Since it is obvious that many changes and modifications can be made inthe above described.

details without departing from the nature and spirit of the invention,it is to be understood that the invention is not to be limited to thedetails pended claims.

I claim: I

described herein except as set forth in the ap- 1. A; flexible,durable," regeneratedgcellulo'se perature of 25 C.

HENRY SHIRLEY ROTHRQCK.

